Preferably, conventional office chairs are designed to provide significant levels of comfort and adjustability. Such chairs typically include a base which supports a tilt control assembly to which a seat assembly and back assembly are movably interconnected. The tilt control mechanism includes a back upright which extends rearwardly and upwardly and supports the back assembly rearwardly adjacent to the seat assembly. The tilt control mechanism serves to interconnect the seat and back assembly so that they may tilt rearwardly together in response to movements by the chair occupant and possibly to permit limited forward tilting of the seat and back. Further, such chairs typically permit the back to also move relative to the seat during such rearward tilting.
The back assembly of such office chairs may have a variety of constructions wherein one type of construction includes an annular back frame which defines an open interior in which the chair occupant's back is supported. This central open area is enclosed by a suspension fabric which spans the opening and has the outer peripheral edge thereof affixed to the annular frame.
The back frame further has a section thereof rigidly connected to an upright of the chair. The upright is connected to a tilt control mechanism, which mechanism supports the seat assembly and governs rearward tilting of the upright. As such, the back assembly moves in combination with the upright when the occupant reclines within the chair.
It is an object of the invention to provide an office chair having a chair back arrangement which is improved relative to prior chair back constructions and specifically is improved relative to the attachment of a suspension fabric to the rigid back frame.
Therefore, the invention relates to an office chair and more particularly, to the construction of a chair back assembly and the process for stretching and attaching the suspension fabric to the back frame in a stretched condition.
The back assembly comprises an annular frame having a suspension fabric which spans the central opening of the back and has the periphery of the suspension fabric connected to the frame. The suspension fabric comprises a single layer of suspension material which connects to the frame by a plastic spline that is press fitted into an annular spline channel formed about the periphery of the back frame.
The back frame is defined by side frame rails, which extend vertically, and transverse cross rails, which extend horizontally between the side rails at the top and bottom thereof. The back frame has a contoured shape wherein the side frame rails curve rearwardly and outwardly in the side-to-side direction, while the cross rails also curve in the front-to-back direction to provide a contoured shape for the back frame that comfortably conforms to the chair back of the chair occupant.
To form the spline channel, the back frame is constructed of molded front and back ring sections which are grooved about their respective peripheries to define front and rear channel portions. The front channel portion defines the front wall of the spline channel while the rear channel portion defines the rear channel wall. The front and rear ring sections overlie each other in opposing relation and are rigidly secured together by suitable fastening means such as ultrasonic welding, adhesives or even threaded fasteners. When the two frame sections are rigidly joined together, the grooved portions align with each other and define the spline channel. In this manner, complex contours may be formed in a molded back frame while still permitting the formation of a spline channel about the periphery thereof.
Once the frame is assembled, the suspension fabric is fastened to the frame by a spline which is press fitted into the spline channel and traps the edge portions of the suspension fabric within this channel.
The attachment structure thereby permits the securement of the suspension fabric to the frame using an elastomeric spline. This fabric is pre-stretched during assembly and then secured to the frame in this pre-stretched condition by the spline.
The process involves securing or assembling the two frame sections together to define a frame unit, and then attaching the fabric thereto. Attachment is accomplished by positioning the frame in the bottom nest of an attachment machine, laying a fabric blank over the frame and stretching the fabric in place by a plurality of stretcher clamps placed about the peripheral edge of the fabric. These peripheral stretcher clamps pull or tension the fabric longitudinally to pretension the fabric.
The fabric is then clamped on the upper surface of the frame by a top nest or clamp head which drops over the bottom nest and has a downward facing clamp surface that clamps the fabric surface onto the opposing frame face. This clamping holds the fabric in a stretched condition. Once clamped by the top nest, the peripheral stretcher clamps are released so that the peripheral edge of the fabric blank hangs loose. Thereafter, a spline tool is run around the spline groove of the frame to simultaneously drive a spline and the fabric edge into the groove about the frame periphery which removes the slack in the peripheral fabric edge and secures the fabric to the frame. When the top nest is removed, the fabric remains in the stretched condition due to the securement by the spline. This provides an improved method for securing a fabric to a contoured chair frame.
The foregoing features provide an improved back frame arrangement, wherein other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.
Certain terminology will be used in the following description for convenience and reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the arrangement and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.